[gmx-users] Problem with Na

[Mauricio Arenas Salinas]

hi All:
i try to do MD for protein with Na and water,  but when 
the EM finishes, the final structure does not 
present/display moleculas of Na. To that can have this? 
and q I can make to solve it?
  topology:

Include forcefield parameters
#include "ffgmx2.itp"

; Include chain topologies
#include "cysk_A.itp"
#include "cysk_B.itp"
#include "ions.itp"

; Include water topology
#ifdef FLEX_SPC
#include "flexspc.itp"
#else
#include "spc.itp"
#endif


#ifdef POSRES_WATER
; Position restraint for each water oxygen
[ position_restraints ]
;  i funct       fcx        fcy        fcz
    1    1       1000       1000       1000
#endif

[ system ]
; Name
Protein in water

[ molecules ]
; Compound        #mols
Protein_A           1
Protein_B           1
SOL             23792
Na                 12


Thank you very much